Malodorous and toxic gases comprise a wide class of gases many of which are oxidizable. Such oxidizable malodorous gases include aromatic compounds (e.g. xylene), ketones (e.g. methylvinyl ketone), esters (e.g. ethoxyethylacetate), mercaptans (e.g. methyl mercaptan), amines (e.g. dimethylamine) and napthalene. Such oxidizable toxic gases include ethylene oxide, isocyanates, benzene, and polycyclic aromatic hydrocarbons. Numerous technologies exist for the removal of such malodorous or toxic gases from industrial exhaust air streams where the concentration of the malodorous or toxic gas is high, for example, where the concentrations are greater than 500 ppm. However, it becomes exponentially more difficult, hence more expensive, to remove such gases as the concentration becomes lower. Yet malodorous gases such as reduced sulphur compounds remain odorous even at concentrations in the order of 1 ppb.
Eliminating malodorous or toxic gases may be achieved by any of a number of known radicals, for example, OH, HO.sub.2, O, O(.sup.3 P), CH.sub.3 O and CH.sub.3 O.sub.2. Of these the most reactive radical, and the most powerful oxidizing agent generally, next to fluorine, is OH. In atmospheric chemistry, reactions involving the OH radical have been found to be the principal removal process for gaseous atmospheric pollutants.
However, to completely remove a malodorous or toxic gas from a high volume industrial exhaust air stream has previously proved difficult. Typically the object was achieved by adding ozone or a similar substance and subjecting the air stream to radiation. Removal efficiency was achieved by arbitrarily increasing the concentration of ozone and the intensity of the radiation in a single reaction zone in the air stream.